On-line Measurement Of Tie-bars Stress In Injection Molding Machine And Its Application In Injection Molding Process

It is of great significance to on-line characterize the tie-bars stress of the injection molding machine,which can prolong the injection molding machine life,improve the injection products quality,reduce the production cost.This paper establishes a new method for on-line measurement of tie-bars stress by ultrasound,and applies it to measure the clamping force and cavity pressure.The ultrasonic method has the advantages of nondestructive,on-line and economical,and it is suitable for industrial application.The main contents are as follows:Firstly,the theory for on-line measurement of tie-bars stress was analyzed and the mathematical model was established.And the calculation means for two key parameters of the ultrasonic method,time difference of ultrasonic propagation and acoustic elasticity coefficient were analyzed and determined.A set of ultrasonic measurement system and a set of auxiliary verification system were designed and established.Secondly,the accuracy and repeatability of the ultrasonic measurement on the tie-bars of injection molding machine was confirmed through the measurement results.And the effects of three parameters on the measurement results were explored.Then,in order to satisfy the industrial commend,the applicability of four practical problems in industrial production,i.e.different sizes of molds,different specifications of injection molding machines,different environmental temperatures and long-term work was analyzed and confirmed.The maximum stress difference square between the ultrasonic method results and strain gauge method results was 2.318(MPa)2,and the maximum stress standard deviation of the ultrasonic method results was 0.080 MPa.Thirdly,a mathematical model for on-line measurement of clamping force by ultrasound was established,and a set of ultrasonic measurement system and a set of auxiliary verification system were established.The clamping force on-line measurement results confirmed the accuracy and repeatability of the ultrasonic method.Furthermore,the ultrasonic method was industrially applied to judge the health of the clamping state.The clamping state health standard was formulated,and an example was given to demonstrate it.The maximum of the standard deviation between the ultrasonic method results and strain gauge method results was 4.319 kN with a deviation of 4.1%.The maximum of the stress standard deviation for the ultrasonic method results was 0.973 kN.Finally,the new principle of cavity pressure measurement by ultrasound was analyzed and the related mathematical model was deduced.The ultrasonic measurement system and auxiliary verification system were established.The cavity pressure on-line measurement results confirmed the accuracy of the ultrasonic method,and the optimization measures were put forward.Meanwhile,the applicability for different clamping forces and injection materials of the proposed method was studied and affirmed.Moreover,the ultrasonic method was applied to measure the industrial production process,including the V/P conversion point and the holding pressure.The cavity pressure measured by ultrasound and pressure sensor is 43.14 MPa and 44.98 MPa,respectively,with a difference of 4.27%.Based on the above research results,a new ultrasonic measurement method for tie-bars stress,clamping force and cavity pressure was put forward.The basic theory was analyzed and the mathematical models and measuring systems were established.The accuracy,repeatability and applicability of the new ultrasonic method were confirmed.The research results of this paper contributes to prolong the injection molding machine life,improve the injection products quality,which have broad application prospects.